Law of Evidence Fundamentals

A debriefing on some key concepts is helpful for trial. A trial lawyer must be well versed in the law of evidence because it impacts most of their work.

Tackling Evidentiary Issues

When faced with an evidence issue, first consult Ontario’s Evidence Act (if it’s a provincial matter such as an action in the Ontario Superior Court of Justice) or the Canada Evidence Act (if it’s a federal matter such as a criminal proceeding).

Second, take a look at the rules of procedure for the forum in which your trial or hearing is proceeding. These may impact admissibility.

Third, consider the common law. Basic common law principles are that evidence must be relevant and material, not subject to a rule excluding the evidence and the probative value must outweigh any prejudice.


It may seem obvious: evidence must be relevant to the case. It is surprising how often irrelevant issues come up at trial.


Even if the evidence is relevant, it must be material, or significant to make it worthwhile for the Court to listen to it. In other words, it is ineffective to bring up relevant but insignificant facts.


Hearsay is testimony about what someone else said happened. For example, witness A testifies about what witness B says B saw. This is generally inadmissible because B should be called as the witness as B observed things first-hand. There are lots of exceptions to the hearsay rule; it is not a hard and fast rule. For example, testimony in another proceeding, admissions, business records and contemporaneous notes can trigger exceptions. If there is important hearsay evidence, a plan to deal with this at trial needs to be made.

Opinion Evidence

Only an expert witness, qualified by the Judge, can give opinion evidence. For example, the value of a business is a matter of opinion requiring a financial expert. Expertise is dependent on appropriate education and/or experience. Expert evidence will require an expert report in compliance with rule 53.

Settlement Discussions

Negotiations, mediations and pre-trials may not be raised at trial. This is due to policy reasons that aim to promote candid settlement discussions. Marking letters and emails “without prejudice” is helpful, but the content of the communication is what matters. For communication to be truly “without prejudice,” it must be in contemplation of or during litigation, have a settlement purpose and the intention must be that it is not to be shared if settlement falls does not happen.

Other Exclusions

Other exceptions exist relating to issues such as character evidence, confessions to authorities, information obtained from a confidential relationship and Charter violations. If you want to keep evidence out, research on exceptions is recommended.

Prejudice vs. Probative Value

The admission of evidence can be blocked if the probative value is slight and the prejudice of the evidence is significant. This comes up more often in criminal matters than in civil matters.

Credibility and Cross-Examination

A great deal of leeway is granted on cross-examination. A witness may not be cross-examined on collateral facts, but they can be cross-examined on prior inconsistent statements. For example, if the case is about an auto accident witnessed by a plumber, challenging the witness by suggesting they are not a good plumber and therefore not credible is a collateral attack. But the witness can be questioned about what the witness said they saw to another person, which would otherwise be hearsay.

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